Project Summary The mechanisms of cyst formation in autosomal dominant polycystic kidney disease (ADPKD) remain incompletely understood and the effective clinical therapies for ADPKD are not available. My long-term career goal is to establish an independent translational research laboratory, where I will elucidate the mechanisms of cyst formation and growth, and discover novel therapeutic strategies for ADPKD. This NIDDK Mentored Research Scientist Development (K01) application proposes a multidisciplinary 5- year training program to provide the candidate Dr. Xia Zhou with the experience and resources necessary to launch a successful career. The training plan, developed closely with primary mentor Dr. Xiaogang Li and co-Mentor Dr. James Calvet will strengthen my previous expertise in the epigenetics and ADPKD research by advancing my knowledge and technologies related to the study of DNA methylation and histone acetylation. The very stimulating scientific environment at University of Kansas Medical Center will not only provide me with the expertise and facilities necessary for successful completion of this project, but will also prepare me to transition smoothly into an independent faculty position. The objective of the proposed study is to understand the functional roles of a key epigenetic regulator, DNA methyltransferase 1 (DNMT1), in ADPKD. Our preliminary studies indicated that DNMT1 was upregulated in Pkd1 mutant renal epithelial cells and tissues, and that treatment with DNMT1 inhibitors, 5-azacytidine and hydralazine, delayed cyst growth in Pkd1 conditional knockout mice. Our previous study showing that upregulation of SIRT1 contributes to cyst development through regulating cystic renal epithelial cell proliferation and death in ADPKD animal models suggests a promising therapeutic strategy for ADPKD treatment by using nicotinamide (vitamin B3). SIRT1 has been found to deacetylate DNMT1 and increase its methyltransferase activity. Thus, we hypothesize that upregulation of DNMT1 regulates cystic renal epithelial cell proliferation through STAT3 activation and regulates apoptosis through p53 signaling, and targeting DNMT1 delays renal cyst growth in vivo in orthologous murine models of ADPKD, and that DNMT1 synergizes with SIRT1 to regulate cyst growth in ADPKD, and targeting both SIRT1 and DNMT1 would delay cyst growth further in ADPKD. We will test this hypothesis with three specific aims. In specific aim 1, we will 1) investigate whether DNMT1 regulates cystic renal epithelial cell proliferation through SHP-1 mediated phosphorylation and activation of STAT3; and 2) investigate whether DNMT1 regulates apoptosis through the p53 dependent pathway. In specific aim 2, we will 1) test whether knockout of DNMT1 delays renal cyst growth in Pkd1 knockout mice; and 2) test whether inhibition of DNMT1 with 5-azacytidine or hydralazine delays renal cyst growth in Pkd1 knockout mouse models. In specific aim 3 we will 1) investigate whether SIRT1 regulates the activity and stability of DNMT1 in cystic renal epithelial cells; and 2) investigate whether SIRT1 regulates the methylation status of SHP-1, and whether DNMT1 regulates histone acetylation of SHP-1; and 3) test whether inhibition of both DNMT1 and SIRT1 synergistically delays cyst growth in Pkd1 knockout mice. This is the first study to define the functional roles of DNMT1 and DNMT1-mediated signaling pathways in cyst development in ADPKD, which will not only further our understanding of cyst development but also provide a rationale for using DNMT1 inhibitors as a therapy for ADPKD. In addition, this study will reveal the relationship between DNMT1- mediated methylation and SIRT1-mediated acetylation in regulating cyst development, and will help promote the development of novel therapeutic approaches targeting both DNMT1 and SIRT1.